Power converter system having active standby mode and method of controlling the same

ABSTRACT

A power system having a plurality of operating modes including an active mode and an active standby mode includes a power converter and a controller the power converter is configured to adapt a power supply to a desired output, and the power converter includes a plurality of semiconductor switches that receive a gating signal when the power system is in the active mode such that the power converter is in a gating state. The controller controls the power converter in the active mode and the active standby mode, and the controller is configured to: while the power converter is synchronized to the grid, determine whether the power system should enter into the active standby mode in which the power converter is in a non-gating state; when it is determined the power system should enter into the active standby mode, control the power converter to be in a non-gating state such that the power system is in the active standby mode.

RELATED APPLICATIONS

The present patent document claims the benefit of the filing date under35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No.62/188,282, filed Jul. 2, 2015, which is hereby incorporated byreference.

DESCRIPTION Field of the Invention

The present invention relates generally to an electric power converterfor power conversion between a power source and a grid; and morespecifically, to an electric power converter having a plurality ofoperating modes including an active standby mode, and a method ofcontrolling the same.

BACKGROUND

A power system may include distributed power sources (e.g., distributedgenerators, battery banks, and/or renewable resources like solar panelsor wind turbines to provide power supply to a grid (e.g., a microgridhaving local loads and/or a utility grid). The power system may includea power converter, such as a power inverter, for converting powerbetween a power source and a grid. Such power conversion may includeAC/DC, DC/DC, AC/AC and DC/AC.

A micro-grid system can include a variety of interconnected distributedenergy resources (e.g., power generators and energy storage units) andloads. The micro-grid system may be coupled to the main utility gridthrough switches such as circuit breakers and/or contactors. In theevent that micro-grid system is connected to the main utility grid, themain utility grid may supply power to the local loads of the micro-gridsystem. The main utility grid itself may power the local loads, or themain utility grid may be used in combination with the power sources ofthe micro-grid to power the local loads.

A controller comprising hardware and software systems may be employed tocontrol and manage the micro-grid system. Furthermore, the controller isable to control the on and off state of the switches so that the microgrid system can be connected to or disconnected from the main gridaccordingly. The grid connected operation of the micro-grid system iscommonly referred to as “grid tied” mode, whereas the grid disconnectedoperation is commonly referred to as “islanded” or “stand alone” mode. Amicro-grid system in grid tied mode should be capable of disconnectedfrom the main grid and transitioning to islanded mode in the case of agrid event in which abnormal operation conditions, such as a poweroutage, occur at the main utility grid.

When the micro-grid includes a battery bank, a battery energy storagesystem may be used to provide power to, or to receive power from, themicro-grid. The battery energy storage system can be used as an energystorage unit in a smart grid system. Renewable energy sources such asphotovoltaic/solar panels and wind turbines are intermittent sourcessubject to unpredictable and inconvenient weather patterns. Thegeneration source rarely matches the load needs; and therefore, it isdesirable to provide energy storage units. The use of energy storageunits, which can both store and supply power, allows the micro-gridsystem to provide reliable and stable power to local loads.

The energy storage units can also store excess energy from the renewablesources (and potentially the grid). For example, renewable energygeneration may exceed load demand of the micro-grid. Without energystorage capability, the extra generation is lost. If energy storageunits are employed in the micro-grid, the extra generation can becaptured by storing it in the batteries. The energy storage units canthen supply this power to local loads and even the main utility gridwhere appropriate.

In a power system such as the battery energy storage system describedabove, the power source or storage unit is not constantly providingpower. For example, in the case of a battery bank providing gridstability services such as automatic voltage response, the batteries maybe neither discharging nor charging. Power systems, such as the batteryenergy storage system discussed above, have an “off” and an “on” state.During the “off” state, the switches are open and the inverter is notsynchronized to the grid. Thus, the “off” state can be used to conservepower when the battery bank is neither charging nor discharging.However, the switches are mechanical or electromechanical switches suchas contactors. Thus, when the system needs to operate (e.g., power needsto be supplied to or from the battery), the startup time is limited bythe closing time of these mechanical switches, which may be up toseveral hundred milliseconds or several utility voltage cycles. A delayof this magnitude is undesirable to a user of the power system.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include an electric powerconverter, system and control method having a plurality of operatingmodes including an active standby mode for improving the response timeand energy savings of an inverter system.

In one aspect, a power system having a plurality of operating modesincluding at least an active mode and an active standby mode includes apower converter and a controller. The power converter is configured toadapt a power supply to a desired output, and the power converterincludes a plurality of semiconductor switches that receive a gatingsignal when the power system is in the active mode such that the powerconverter is in a gating state. The controller controls the powerconverter in the active mode and the active standby mode, and thecontroller is configured to: while the power converter is synchronizedto the grid, determine whether the power system should enter into theactive standby mode in which the power converter is in a non-gatingstate; when it is determined the power system should enter into theactive standby mode, control the power converter to be in a non-gatingstate such that the power system is in the active standby mode.

The power converter may be coupled between the power source and a powerinverter, and the controller may determine whether the power systemshould enter into the active standby mode while the power inverter issynchronized to a grid.

The power converter may be a power inverter coupled between the powersource and a grid, and the controller may determine whether the powersystem should enter into the active standby mode while the powerinverter is synchronized to the grid.

The power system may also comprise a power source side switch coupledbetween the at least one power source and the power converter and a gridside switch coupled between the at least one power source and a grid,with the power source side switch and the grid side switch being closedin both the active mode and the active standby mode.

The power system may also have a power inverter coupled between thepower source and the grid, and the controller may be configured toinitialize the power inverter. In initializing the power convert, thecontrol controller may be configured to: charge a DC bus from at leastone power source; close the power side switch; synchronize the powerconverter to the grid; enter the power converter into the gating state;close the grid side switch between the power converter and grid, therebyentering the power system into a grid tied mode; and initialize theactive standby mode to the off mode.

The at least one power source may be an energy storage unit, and thepower system may operate in a discharge state, a charge state, and anidle state. Within the discharge and charge states, the controllercontrols the power converter to discharge and charge the energy storageunit. The controller may then determine that the power system shouldenter into the active standby mode when the power system is in an idlestate.

The controller may determine whether the power system should enter in tothe active standby mode by comparing the power command to apredetermined threshold, and making the determination based on thecomparison.

The predetermined threshold may include upper and lower thresholdvalues. In this case, the controller may compare the power command tothe lower threshold value when determining whether to enter into activestandby mode, and compare the power command to the upper threshold valuewhen determined whether to enter into active mode.

The controller may determine whether the power system should exit theactive standby mode and enter the active mode by continuing to comparethe power command to the predetermined threshold, and if the powercommand exceeds the predetermined threshold, control the power converterto be in the gating state.

The controller may be configured to determine whether the power systemshould enter into the active standby mode by determining whether thepower system is in a charge or discharge state (e.g., whether a powercommand is positive or negative). When the power system is determined tobe in a charge state, the controller may compare the power command to afirst predetermined threshold, and when it's determined that the powercommand is higher than the predetermined threshold, the controller maydetermine that the power system is in an idle state and should enterinto active standby mode. When the power system is determined to be inthe discharge state, the controller may compare the power command to asecond predetermined threshold. When it's determined that the powercommand is lower than the second predetermined threshold, the controllermay determine that the power system is in an idle state and should enterinto active standby mode.

The first predetermined threshold may include an upper first thresholdvalue and a lower first threshold value; and the second predeterminedthreshold may include an upper second threshold value and a lower secondthreshold value. When it is determined that the power system is in thecharge state, the power command is compared to the lower first thresholdvalue to determine whether to enter the active standby mode, and thepower command is compared to the upper first threshold value todetermine whether to enter the active mode. When the power system isdetermined to be in the discharge state, the power command is comparedto the lower second threshold value to determine whether to enter intothe active standby mode, and the power command is compared to the uppersecond threshold value to determine whether to enter into the activemode.

The power system may also comprise one or more sensors coupled betweenthe power converter and the grid to measure real and reactive power,where the power command is determined based on the real and reactivepower measured by the one or more sensors.

The power system may also comprise a controller that is furtherconfigured to receive a user command from a master controller to enterinto standby mode and determine that the power system should enter intoactive standby mode when the user command is received.

The controller may be configured to perform an AND operation on the gatesignal and the result of the determination as to whether the powersystem should enter into the active standby mode.

The power converter may be coupled between at least one power source anda utility grid, and the power converter may be electrically coupled to amicrogrid have one or more local loads. The power controller may befurther configured to: determine when a grid event occurs in the utilitygrid; open an islanding switch to disconnect the power converter fromthe utility grid when it is determined that the grid event occurs; andenter into the active mode such that the power converter is gating thesupply power to one or more local loads if the power system is in activestandby mode when the grid event occurs.

The controller may be configured to: determine whether the system shouldenter the active standby mode; compare a grid frequency to apredetermined threshold; and determine whether the power system shouldenter active standby mode according to the comparison.

In another aspect, a method of controlling a power system in a pluralityof operating modes, including at least an active mode in which a powerconverter is synchronized to a grid and is in a gating state and anactive standby mode in which the power inverter is synchronized to thegrid and not in a gating state, includes: comparing a power command to apredetermined threshold, and determining whether the system should enterinto the active standby mode based on the comparison; and when it'sdetermined that the system should enter into the active standby mode,controlling the power converter to be in a non-gating state.

Prior to comparing the power command to the predetermined threshold, themethod may further comprise initializing the power converter, theinitializing comprising: synchronizing the power converter to the grid;entering the power converter into the gating state; closing a switchcoupled between the power converter and grid such that the power systemis in grid-tied mode; and initializing active standby mode to off.

The method that may further comprise: after determining the power systemshould enter into active standby mode, continuing to compare the powercommand to the predetermined threshold in order to determine whether thepower system should exit the active standby mode and enter the activemode

Comparing a power command to a predetermined threshold and determiningwhether the power system should enter into active standby mode based onthe comparison may comprise: determining the charge or discharge stateof the power system and determining the positivity or negativity of thepower command; when it's determined that the power system is in thecharge state, comparing the power command to the first predeterminedthreshold, and when it's determined that the command is higher than thethreshold, determining that the system should enter active standby mode;when it's determined that the system is in the discharge state,comparing the power command to a second predetermined threshold, andwhen it's determined that the command is lower than the secondthreshold, determining that the system should enter active mode.

The method may further comprise receiving the power command from aseparate master controller.

The method may further comprise: determining when a grid event occurs;when said grid event occurs, opening an islanding switch to disconnectthe power inverter from the grid; and if the system is in active standbymode when the grid event occurs, entering into the active standby suchthat the power inverter is gating to supply power to a local load.

In another aspect, a power inverter system operating in a plurality ofmodes including at least an active and an active standby mode comprisesa power inverter and a controller. The power inverter converts powerbetween a power source and a grid, and the power inverter may comprise aplurality of semiconductor switches receiving a gate signal whenoperating in the active mode such that the power inverter in is a gatingstate. The controller controls the power inverter in the active andactive standby modes, and the controller may be configured to:synchronize the power inverter to the grid; control the power inverterto be in the gating state in the active mode so that the semiconductorswitches receive the gate signal; determine whether the power invertershould enter into active standby mode in which the inverter is in anon-gating state; and when in active standby mode, control the powerinverter to be in a non-gating state.

The plurality of semiconductor switches may comprise at least one ofinsulated gate bipolar transistors, silicon carbide devices and MOSFETs.

The controller may be configured to determine whether the power invertershould enter the active standby mode by comparing a power command to apredetermined threshold, and determining whether the inverter shouldenter the active standby mode according to the comparison.

While the power inverter is in the active standby mode, the controllermay compare the power command to the predetermined threshold todetermine whether the inverter should exit the active standby mode andenter active mode.

The controller being configured to determine whether the power invertershould enter into the active standby mode may include the controllerbeing configured to: determine whether a power command is positive ornegative; when the command is negative, compare the command to a firstpredetermined threshold, and when the command is higher than thethreshold, determine that the inverter should enter into active standbymode; when the power command is positive, compare the command to asecond predetermined threshold, and when the command is lower than thesecond threshold, determine that the inverter should enter into activestandby mode.

The controller may be configured to receive a user command from a mastercontroller to enter standby mode, and determine that the power invertershould enter the active standby mode when the command is received.

A power inverter system in which the controller may also be configuredto perform an AND operation on the gate signal and determine whether theinverter should enter the active standby based on the result of thedetermination.

The controller may be further configured to; determine when a grid eventoccurs; if the inverter is in active standby mode when it determinedthat said grid event occurs, enter into the active mode such that theinverter is gating to supply power to a local load.

The controller may be configured to compare a grid frequency to apredetermined threshold, and determine whether the system should enterinto the active standby mode according to the comparison.

BRIEF DESCRIPTION OF THE FIGURES Non-Limiting Embodiments of theDisclosure

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings, wherein:

FIG. 1A is an electrical schematic diagram illustrating a power systemaccording to an embodiment of the present invention. FIG. 1B is anelectrical schematic diagram illustrating the circuitry of the powerconverter and the inductor of the filter shown in FIG. 1A.

FIGS. 2A and 2B illustrate a method of controlling the power systemaccording to an embodiment of the present invention in which the powersystem implements a plurality of operating modes while the powerconverter is synchronized to the grid. FIG. 2A is a method forinitializing the power converter 200, during which the power converteris synchronized to the grid. FIG. 2B is a method of implementing theplurality of operating modes.

FIG. 3 illustrates a method of controlling the power system according toan embodiment of the present invention in which the power system isconnected to an energy storage unit and implements a plurality ofoperating modes.

FIG. 4 illustrates a method of controlling the power system according toan embodiment of the present invention in which the power systemoperates in grid-tied mode and islanded mode.

FIG. 5A is an electrical schematic diagram illustrating a power systemaccording to an embodiment of the present invention. FIG. 5B is anelectrical schematic diagram illustrating the circuitry of the powerconverter shown in FIG. 1A.

FIG. 6 illustrates a control scheme for comparing the power command to adeadband and entering/leaving a gating state.

DETAILED DESCRIPTION

Reference will now be made to detailed embodiments, examples of whichare illustrated in the accompanying drawings. In the following detaileddescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. However, it will beapparent to one of ordinary skill in the art that the present inventionmay be practiced without these specific details. In other instances,well-known methods, procedures, and components have not been describedin detail so as not to unnecessarily obscure aspects of the embodiments.

In the following description of the invention, certain terminology isused for the purpose of reference only, and is not intended to belimiting. For example, although the terms first, second, etc. may beused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. As used in the description of the invention andthe appended claims, the singular forms “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will also be understood that the term “and/or”as used herein refers to and encompasses any and all possiblecombinations of one or more of the associated listed terms. It will befurther understood that the terms “comprises” and/or “comprising,” whenused in this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps operations, elements, components, and/or groups thereof.

FIG. 1A is an electrical schematic diagram illustrating a power system100 according to an embodiment of the present invention. FIG. 1B is anelectrical schematic diagram illustrating the circuitry of the powerconverter 200 and the inductor of filter 174 shown in FIG. 1A.

Referring to FIG. 1A, a power system 100 according to an embodiment ofthe present invention may include a power converter 200, an input 110,switches 120 and 130, sensors 140 and 150 and a controller 300. Input110 is coupled to a power source (e.g., a power generator or energystorage unit) that supplies power to the power system 100. The input 110is electrically coupled to the power source side switch 120. The powerconverter 200 converts power between the power source coupled to input110 and a grid that is coupled to the power system 100 at gridconnection 160. On the grid side, power converter 200 is coupled to gridside switch 130, and the grid side switch 130 is coupled to a grid atthe grid connection. Power conversion by power converter 200 may includeAC/DC, DC/DC, AC/AC and DC/AC.

In an embodiment, the power converter 200 may be a bi-directional powerinverter that converts power between DC and AC. The inverter 200 mayconvert power between DC and AC and may be controlled in differentschemes. For example, in a grid-tied scheme, the power inverter isconnecting to an established grid (e.g., a utility grid) and isoperating in current source mode. In a grid forming scheme, the inverteris setting or creating the grid and is operating in voltage source mode.

In another embodiment, the power converter may be a power converter 202that is coupled between the power source 110 and another power converter200, such as a power inverter 200. Such an example is shown in FIGS. 5Aand 5B. In this example, power inverter 200 is coupled between the input110 and the grid connection 160, and power converter 202 is coupledbetween the power inverter 200 and the input 110. In the example shownin FIGS. 5A and 5B, the power converter 202 may be a DC/DC powerconverter that provides a voltage source to the power inverter 200. Theflow of energy through the DC/DC power converter 202 is modulated tomaintain an appropriate voltage source to the inverter 200. In anotherembodiment, the power converter 202 may be an AC-DC converter 204coupled to an AC source (e.g., a wind turbine) at input 110. The AC-DCconverter 202 may then be coupled to a DC-AC inverter 200. In thisembodiment, the flow of energy through the AC-DC converter 202 ismodulated to maintain an appropriate voltage source to the inverter 200,and the inverter 200 converts the power to AC suitable for gridconnection 160.

The power system 100 may also include additional elements such as fuse170, manual disconnect switch 172, pre-charge circuit 122, LC filter174, and grid circuit breaker 176. Fuse 170 is for disconnecting input110 from the power converter 200 in the event of a fault. The manualdisconnect switch 172 can be opened manually so that equipment in thepower system 100 can be serviced. Pre-charge circuit 122 may be used topre-charge the DC bus. LC or resonant filter 174 may be configured tofilter the AC output of power converter 200. The AC output of powerconverter 200 may usually contain harmonics and/or noises of otherfrequencies. Output LC filter 200 may be configured to filter out theseharmonics and/or noises. Circuit breaker 176 can be manually opened sothat equipment in power system 100 can be serviced, or circuit breaker176 may open in an over current event to disconnect from the gridconnected to grid connection 160.

The grid connection 160 may be a connection to a micro-grid and/or amain (utility) grid. The micro-grid may include one or more distributedenergy resources (distributed generators and energy storage units) andlocal loads within a local area. When the power system 100 is connectedto the micro-grid through grid connection 160, the power sourceconnected to input 110 is one of the distributed energy resources (i.e.a generator or an energy storage unit) of the micro-grid. The loads canbe one user (e.g., a utility customer), a grouping of several sites, ordispersed sites that operate in a coordinated fashion. The distributedgenerators may include reciprocating engine generators, micro-turbines,fuel cells, photovoltaic/solar panels, wind turbines, etc. Thedistributed energy resources of the micro-grid may be coordinated by amaster (or user) controller 400. The master controller 400 may bephysically separate from the controller 300 of the power system 100, maybe included within the same box, or could be integrated with or includedas part of the controller 300. The local loads of the micro-grid may bepowered by the distributed energy resources of the micro-grid and/or theutility grid to which the micro-grid is connected.

In an embodiment, the power source connected to the input 110 may be anenergy storage unit such as a battery (which could be a battery bankthat includes plural batteries) that both stores and supplies energyfrom/to the grid. In this case, the input 110 is a DC input and thepower converter 200 may be a 3-phase bi-directional power inverter thatconverts DC electric power on the DC side to AC electric power on thegrid side and vice versa.

When the power system 100 is connected to a micro-grid, the batteryconnected to input 110 may store excess energy not needed to power thelocal loads from one or more other distributed energy sources of themicro-grid. The battery may also store energy from the main utilitygrid. Energy stored in the battery connected to the input 110 may besupplied to local loads in the event of an outage at the main utilitygrid. The energy stored in the battery may also be used to provide morereliable and stable power when the micro-grid includes moreunpredictable energy resources such as photovoltaic/solar panels andwind turbines.

The power source side switch 120 may be an electromechanical switch suchas a DC contactor, and the grid side switch 130 may be anelectromechanical switch such as an AC contactor. When power system 100is in an “off” state, the electromechanical switches 120 are opened todisconnect the power converter 200 from the power supply connected toinput 110 and the grid connected to grid connection 160. Conversely,when the power system 100 is in an “on” state, the electromechanicalswitches 120 are closed.

The DC side switch 120 may, for example, be included within the batterycontainer of the battery connected to input 110 or within the powerconverter 200. Alternatively, the switch 120 may be installed as part ofthe site external to both the battery and the power converter 200. Inaddition, the grid side switch 130 may be included within the powerconverter 200 or may be part of the site external to the power converter200.

The power converter 200 and the controller 300 together operate as apower conversion system for converting power between the power sourceand the grid. In an embodiment, the controller 300 is responsible forthe control, monitoring, and measurement of the power system 100 and maycommunicate with a master (or user) controller 400 in the event that thepower system 100 is connected to a micro-grid that is coordinated by amaster (or user) controller. The switches 120 and 130 may be controlledby the controller 300. The switches 120 and 130 may be electricallyoperated by the controller 300 through relay logic. The controller 300uses the sensors 150 between switch 120 and grid connection 160 tomonitor the voltage amplitude, frequency and phase of the grid, and thecontroller 300 uses the sensor 150 between filter 174 and powerconverter 200 to monitor the AC output current amplitude, frequency andphase of the power converter 200. The controller may also monitor DCinput voltage through sensors 140. For sensors 140 and 150, ‘V’ and ‘I’represent a voltage measurement and a current measurement, respectively,‘P’ and ‘PF’ represent power by calculation and power factor bycalculation, respectively, and ‘Hz’ represents a frequency measurement.The sensors 150 may include potential transformers, and the sensors 140may include an isolated voltage monitor.

The controller 300 may be located within the cabinet of the powerconverter 200 or may be a controller that is external to the powerconverter 200. The controller 200 may also include a plurality ofcontrollers that communicate together. When the controller 300 is housedwithin the power converter 200, the controller 300 may be placed in anenvironment that is protected from the power electronics of the powerconverter 200 to mitigate electromagnetic noise interfering with thecontroller's 300 operation. The power electronics of the power converter200 may be actively cooled by forced air and/or liquid, and may becontrolled by controller 300 using fiber optic gating signals orelectrical gating signals.

FIGS. 1B and 5B show embodiments of the power electronics of the powerconverter 200. FIGS. 1B and 5B also show the inductor of the LC filter174. In the embodiment of FIG. 1B, the power converter 200 is abi-directional power inverter; and in the embodiment of FIG. 5B, thepower converter 202 is a DC/DC converter, and the power converter 200 isa power inverter. Referring to FIGS. 1B and 4B, the power converters200, 202 and 204 may include a plurality of semiconductor switches 210.Gates 212 of the semiconductor switches 210 receive gating signals whenthe power converters 200, 202 and 204 are gating (i.e., in a gatingstate). The gate signals are made up of a plurality of switching pulsesfor switching the semiconductor switches 210. The controller 300controls the switching pattern of the semiconductor switches 210 tosynchronize the output of the power converter 200 with the sine wave ofthe grid. In synchronizing the power converter 200 with the grid, thecontroller may control the semiconductor switches to match the phase,amplitude and/or frequency of the inverter to that of the grid. Thesemiconductor switches 210 may, for example, be insulated-gate bipolartransistors (IGBTs). Additional examples of semiconductor switches 210include wide band-gap semiconductor devices such as silicon carbide andmetal-oxide-semiconductor field-effect transistors (MOSFETs).

The power system 100 is not always supplying or receiving power to orfrom the grid, which is referred to as “an idle state”, (i.e. real powerset point=0 kW). To conserve power, the power system 100 may be placedin the “off” state in which switches 120 and 130 are opened todisconnect the power system 100 from the power source and the grid. Inthe “off” state, the power converter 200 is not synchronized with thegrid. However, response time of the power system 100 when transitioningfrom the idle state to a fully charging or discharging state is of greatimportance to a user. The mechanical closure time of these switches maybe up to several hundred millisecond. These closure times serve aslimitations on the response time of the power system 100. Further, aninverter connected to a DC power source needs to pre-charge the DC busprior to closing the mechanical switches. This pre-charging operationcan further limit the response time by as much as 2 seconds.

One solution to the limitations imposed by the closure time of switches120 and 130 is to leave the power system 100 connected to the powersource and the grid, so that the switches 120 and 130 remain closed. Thepower converter 200 is then controlled by controller 300 to a set pointof 0 kW, meaning that the power converter 200 is controlled to output nopower (i.e., 0 kW and 0 kVAR). In this case, the power system 100 canquickly respond to requests even when in an idle state. Taking theexample in which the input 110 is connected to a battery and the gridconnection 160 is connected to a micro-grid in which a wind turbine isan energy resource, the power system 100 is able to quickly respond to acommand to charge the battery (e.g., a sudden gust of wind) or dischargethe battery (e.g., decrease in wind resource).

Although this solution solves the problems associated with the closuretime of the switches 120 and 130, the power converter 200 is stillgating even when the power converter 200 is controlled to output nopower. When gating, the gates 212 are still receiving a gating signal,and thus the semiconductor switches 212 are still switching.Accordingly, the power system 100 is still incurring losses even thoughpower is not being processed, and these losses are supplied by energyfrom the battery. In addition, the power converter's 200 cooling systemmay need to be run to remove the losses from the semiconductor switches212.

FIGS. 2A and 2B illustrate a method of controlling the power system 100according to an embodiment of the present invention in which the powersystem 100 implements a plurality of operating modes while the powerconverter 200 is synchronized to the grid. FIG. 2A is a method forinitializing the power converter 200, during which the power converter200 is synchronized to the grid. FIG. 2B is a method of implementing theplurality of operating modes. FIGS. 2A and 2B illustrate a method ofimplementing the plurality of operating modes in a bi-direction powerinverter that is coupled between a DC power source and an AC grid.However, it should be understood the input and grid connection are notlimited to being a DC input and an AC grid connection. For example,input 110 may be a DC or AC input and output may be a DC or AC gridconnection. In addition, instead of the grid connection, the powerconverter may be a power converter 202 that is connected to anotherpower converter 200, such as in the example shown in FIG. 4A.

Referring to FIG. 2A, prior to synchronizing to the grid, the controller300 may perform an analysis to determine whether the power converter 200is ready to run (step 500). The analysis may include checking to ensurethat there are no faults within the power system 100 and any safetyparameters check out. Upon receipt of a start command (step 510), thecontroller synchronizes the power converter 200 to the grid (step 520).The start command may be a command received from master controller 400,input by a user or autonomously generated by the controller 300. Insynchronizing the controller to the grid, the controller 300 controlsthe switching pattern of the semiconductor switches 210 of the powerconverter 200 to synchronize the output of the power converter 200 withthe sine wave of the grid. When the power converter 200 is coupled to aDC power source at input 110, the controller may then control the powersystem to pre-charge the DC bus (step 530). In pre-charging the DC bus,the power system 100 gently brings the DC voltage up from the DC powersource prior to closing the switch 120 connecting the power converter200 to the input 110. The controller may then close the DC switch 120 soas to energize the battery with the DC port. Upon closing the AC switch130 connecting the power converter 200 to the grid connection 160 (step550), the power converter 200 is ready to enter into active mode duringwhich the power converter 200 is gating and can output an AC voltage.

Referring to FIG. 2B, controller 300 may first determine whether thepower converter 200 should be in active mode (power converter 200 isgating) or active standby mode (power converter 200 is not gating) (step560). Step 560 may be an initial determination made by the controller300 as to whether the power system 100 should be in the active mode orthe active-standby mode. In an alternative embodiment, the controller200 may initialize the power system 100 in the active mode, in whichcase step 560 would be a determination as to whether to remain in activemode or enter into active-standby mode.

In determining whether the power converter 200 should be in active modeor active-standby mode, the controller 300 compares a power command to apredetermined deadband (or threshold) to determine whether the powercommand is within or outside of the deadband. The deadband may be setaccording to any number of ways, including, for example, being set bythe user based on a requirement imposed by a regulating authority orbeing set as a result of a system impact study, which is a technicalanalysis of the local grid/power system.

The power command may be a command for the power inverter 200 tosupply/absorb power, and the power command is the value that is comparedto the deadband to determine whether to enter into the active mode orthe active-standby mode. The power command may be a command received bythe controller 300 from a master controller 400 or may be a command thatis generated autonomously by controller 300 based, for example, onmeasurements taken from sensors. Furthermore, the power command may be avalue calculated by the controller 300 based on measurements or valuesreceived from the master controller 400. The power command is preferablythe amount of real power ‘P’ that the power converter 200 is commandedto supply or absorb, to/from the grid. However, it should be understoodthat the power command is not limited to real power, and the powercommand may be a real power command P or a reactive power command Q oreven an apparent power command.

When the controller 300 is receiving commands from a master controller400, it is preferable that the commands to controller 300 are real power(P) and reactive power (Q) commands within the rating of the inverterboth independently and when added in quadrature to not exceed theapparent power rating of the inverter. The real power command P andreactive power command Q may be commands that are received by thecontroller 300 from a master controller 400 that is coordinating variousenergy resources of a micro-grid. In this case, the real power command Pand reactive power command Q may be calculated based on various factors,such as the needs of the local loads and the output power of the energyresources of the micro-grid. Alternatively, the real P and reactive Qpower commands may be autonomously generated by the controller 200 by,for example, calculating both the real and reactive power needs based onthe measurements taken by sensors 150.

If the power command is within the deadband, the controller 300 controlsthe power converter 200 so that it is not gating, whereby the powersystem 100 enters into the active-standby mode (step 560—NO). While thepower system 100 is in the active-standby mode, the controller 300continues to compare the power command to the deadband to determine ifthe power command falls outside the deadband. If the power command isoutside the deadband, the controller 300 may control the power converter200 so that it is gating, whereby the power system 100 enters intoactive mode (step 570). Once the power system 100 enters into the activemode, the controller 300 continues to monitor the power command todetermine whether it falls within the deadband (step 580). If, while inactive mode, the power command falls within the deadband, the powersystem 100 enters into active-standby mode, during which the controller300 controls the power system 200 so that it is not gating. The powersystem 100 may also employ hysteresis to prevent rapid switching betweenthe active and active-standby modes.

FIG. 6 illustrates a control scheme for comparing the power command to adeadband and entering/leaving a gating state. The semiconductor switches212 may be controlled by pulse width modulated signals output from apulse width modulator (PWM). As shown in FIG. 6, the result of thecomparison 620 between the power command and the deadband is input intoone of the inputs of the AND gate. The other input of the AND gatereceives one of the outputs of the pulse width modulator 600. When powercommand falls outside of the deadband, the output of the comparison 620is a logic high value (or 1), and the output of the AND gate 610 matchesthe output of the PWM 600. When the power command is within thedeadband, the output of the comparison 620 is a logic low (or 0) value,so that the IGBTs 210 do not receive the gating signal output by the PWM600. The control scheme of FIG. 6 may be a comparison that happenswithin the firmware of controller 300, or may be part of the controllogic implemented by controller 300.

Referring again to FIG. 2B, the method may also include a step ofreceiving a stop command (step 590), which may be a command from themaster controller 400 or a command entered by a user. If a stop commandis received (step 190), the power converter 200 stops operation.

The controller 300 controls power system 100 to synchronize the powerconverter 200 to the grid and to transition the power system 100 betweenthe active mode and the active-standby mode. The controller 200 may be afield-programmable gate array (FPGA) or a digital signal processing(DSP) based controller. However, it should be understood that thecontroller 200 is not limited to these two types of controllers.

The following control logic illustrates an exemplary embodiment in whichcontroller is performing initialization of the power system 100 when thepower system 100 is coupled to a DC power source at input 110.

  while(grid_ok = 1 and state = ready)  if (command = start)  state =starting  endif endwhile while(grid_ok = 1 and state = starting)  closedc_precharge;  wait(precharge_time);  if(Vdc>Vdc,min)  close dc_main; endif  start grid_sync;  start gating;  close ac_contactor;  state =runPQ;  active_stdby = OFF; endwhile

In the above control logic, ‘while(grid_ok=1 and state=ready)’ checkswhether the grid voltage and frequency are within bounds and the powerconverter is in a ready state. ‘while(grid_ok=1 and state=starting)’ isthe starting sequence of the power system 100. ‘close dc_precharge’closes a relay to gently charge the dc bus from the power source.‘if(Vdc>Vdc,min)’ checks that the DC bus is charged. ‘close dc_main’closes the dc switch 120. ‘start grid_sync’ synchronizes the powerconverter's controls system to the grid. ‘start gating’ starts switchingof the semiconductor devices to emulate the grid voltage. ‘closeac_contactor’ closes the grid side switch 130. ‘state=runPQ’ indicatesthat the control system 100 is running in grid-tied mode.‘active_stdby=OFF’ initializes active standby to OFF.

The following control logic illustrates an exemplary embodiment in whichcontroller is comparing a power command to a threshold and operating thepower converter 200 in the active and active standby modes. In theexemplary control logic, both real and reactive power commands arecompared to an active standby turn off threshold. However, it should beunderstood that, in alternative embodiments, only one of the real andreactive power commands may be compared to the threshold, or an apparentpower command calculated using real and reactive power commands may becompared to a deadband. In addition, in the below control logic, theactive-standby turnoff threshold to which the power command is comparedincludes an upper value and a lower value. The power command is comparedto the lower threshold value when determining whether to enter intoactive standby mode, and the power command is compared to the upperthreshold value when determining whether to enter into active mode.Having different upper and lower threshold values prevents rapidswitching between the active and active-standby modes.

while(state=runPQ and grid_ok=1)  if(sqrt(Pcmd_usr{circumflex over( )}2+Qcmd_usr{circumflex over ( )}2) <= InverterRating) controlP(Pcmd_usr);  controlQ(Qcmd_usr);  else controlQ(sqrt(InverterRating{circumflex over ( )}2-Pcmd_user{circumflexover ( )}2))//this  example P has priority over Q  endif  if(Pcmd_usr >= SupkW or Qcmd_usr >= SupkVAR)  active_stdby = OFF;  elseif(Pcmd_usr <= SlokW and Qcmd_usr <= SlokVAR)  active_stdby = ON;  endif if (active_stdby = ON)  stop gating;  endif  if(active_stdby = OFF) start gating;  endif endwhile

In the above control logic, ‘while(state=runPQ and grid_ok=1)’ refers tothe power system 100 running in grid-tied mode.‘sqrt(Pcmd_usr̂2+Qcmd_usr̂2)’ is calculation of the apparent power commandusing a real power command and a reactive power command (in thisexemplary embodiment, the real and reactive power commands are userpower commands that may be received by controller 300 from mastercontroller 400). ‘if(Pcmd_usr>=SupkW or Qcmd_usr>=SupkVAR)’ checks ifthe real power command is greater than an upper value of the real activestandby turn off threshold (if the power command is greater than thethreshold, the power command is outside the deadband) or if the reactivepower command is greater than an upper value of the reactive activestandby turnoff threshold; ‘if(Pcmd_usr<=SlokW and Qcmd_usr<=SIokVAR)’checks if the real power command P is less than the a lower value thereal active standby turn off threshold and if the reactive power commandQ is less than a lower value of the real active standby turn offthreshold (if the power command is less than the threshold, the powercommand is within the deadband); ‘if (active_stdby=ON)’ turns offsemiconductor switch gating; ‘if(active_stdby=OFF)’ turns onsemiconductor switch gating; and ‘controlP(Pcmd_usr)’ and‘controlQ(Qcmd_usr)’ are routines to control the active and reactivepower of the power converter 200 to be the power command.

In the above exemplary embodiment, the power command is compared to thedeadband or threshold by the controller 300. In another embodiment, itis possible to receive a standby command from a separate mastercontroller 400. Controller 300 receives the standby command from mastercontroller 400 and controls the power converter 200 to be inactive-standby mode. This embodiment may be advantageously used in amicro-grid in which master controller 400 is coordinating a variety ofdistributed energy resources. In such a case, it may be desirable forthe master controller to directly instruct the power system 100 to enterinto active-standby mode. Exemplary control logic for the controller 200receiving a standby command directly from master controller 400includes:

  while(state=runPQ and grid_ok=1)  start gating;  if (command = stdby) state = standby  endif  controlP(Pcmd_usr);  controlQ(Qcmd_usr);endwhile while(state=standby and grid_ok=1)  stop gating;  Pcmd_usr = 0; Qcmd_usr = 0;  if (command = runPQ)  state = runPQ;  endif endwhile

In the above control logic, ‘start gating’ is a start gating sequence toallow restarting of gating when coming back to active mode from acommanded active standby mode. ‘if (command=stdby)’ changes toactive-standby mode when a user commands a standby. ‘if (command=runPQ)’changes to active mode when commanded by the user so that the powerconverter 200 begins gating.

FIG. 3 illustrates a method of controlling the power system 100according to another embodiment of the present invention in which thepower system 100 is connected to an energy storage unit, such as abattery, and implements a plurality of operating modes while the powerconverter is synchronized to the grid. The initialization method for thecontrol system in this embodiment may be the same as that shown in FIG.2A and will be omitted for brevity.

FIG. 3 refers to an embodiment in which the power system 100 is coupledto an energy storage unit such as a battery at input 110. When the powersystem 100 is coupled to an energy storage unit, the power system 100has both charge and discharge capabilities. In the embodiment shown inFIG. 3, separate thresholds are provided for charge mode and dischargemode. The separate thresholds are the upper and lower bounds of thedeadband.

The controller may first determine whether the power converter 200should be in active mode (power converter 200 is gating) oractive-standby mode (step 300, 310 and 312). Steps 300, 310 and 312 maybe an initial determination made by the controller 300 as to whether thepower system 100 should be in the active mode or the active-standbymode. In an alternative embodiment, the controller 200 may initializethe power system 100 in the active mode, in which case steps 300, 310and 312 would be a determination as to whether to remain in active modeor enter into active-standby mode.

In determining whether the power converter 200 should be in active modeor active-standby mode, the controller determines whether the powercommand is positive or negative (step 300). A power command that ispositive indicates discharge mode, and a power command that is negativeindicates charge mode. When the power command is negative (charge mode)the power command is compared to a first threshold (step 310). When thepower command is greater than the first threshold, the controller 300determines that the power system 100 should enter into theactive-standby mode in which the power converter 200 is not gating (step310—NO), and the controller 300 continues to monitor the power commandto determine whether it becomes lower than the first threshold. If thepower command is lower than the first threshold, the controller 300determines that the power system 100 should be in active mode and thatgating should continue/begin (step 320).

Once the power system 100 enters into the active mode, the controller300 continues to monitor the power command to determine whether it isgreater than the threshold and the power system 100 should enter intothe active-standby mode (step 330—NO). The method may also include astep of receiving a stop command (step 340), which may be a command fromthe master controller 400 or a command entered by a user. If a stopcommand is received, the power converter 200 stops operation.

When the power command is positive (discharge mode), the power commandis compared to a second threshold (step 312). When the power command isless than the second threshold, the controller 300 determines that thepower system 100 should enter into the active-standby mode in which thepower converter 200 is not gating (step 312—NO), and the controller 300continues to monitor the power command to determine whether it becomesgreater than the second threshold. If the power command is greater thanthe second threshold, the controller 300 determines that the powersystem 100 should be in active mode and that gating shouldcontinue/begin (step 322).

Once the power system 100 enters into the active mode, the controller300 continues to monitor the power command to determine whether it isless than the threshold and the power system 100 should enter intoactive-standby mode (332—NO). The method may also include a step ofreceiving a stop command (step 342), which may be a command from themaster controller 400 or a command entered by a user. If a stop commandis received, the power converter stops operation.

The following control logic illustrates an exemplary embodiment in whichthe controller is determining whether a power command is a chargecommand or a discharge command and comparing a power command to one of afirst (charge) threshold and a second (discharge) threshold based on thedetermination. Similar to the above exemplary embodiment, the powersystem 100 may be initialized in the active mode. In the below exemplaryembodiment, each of the first and second thresholds include upper andlower values to prevent rapid switching between active andactive-standby modes. In the below exemplary embodiment, the powercommand is a real power (P) command.

  while(state=runPQ and grid_ok=1)  if (Pcmd_usr <= 0)  if (Pcmd_usr <Pchg_up)  active_stdby = OFF;  elseif (Pcmd_usr > Pchg_lo)  active_stdby= ON;  endif  else  if (Pcmd_usr > Pdis_up)  active_stdby = OFF;  elseif(Pcmd_usr < Pdis_lo)  active_stdby = ON;  endif  endif  if (active_stdby= ON)  stop gating;  endif  if(active_stdby = OFF)  start gating;  endif controlP(Pcmd_usr);  controlQ(Qcmd_usr); endwhile

In the above control logic, ‘while(state=runPQ and grid_ok=1)’ refers tothe power system 100 running in grid-tied mode. ‘if(Pcmd_usr<=0)’ checksif the power command is negative, in which case the power system 100 isin charge mode. ‘if (Pcmd_usr<Pchg_up)’ checks, when in charge mode, ifthe power/charge command is less than an upper value of a first (charge)threshold (this means that more charge is commanded since the chargeconvention is negative power). ‘elseif (Pcmd_usr>Pchg_lo)’ checks, whenin charge mode, if the charge command is higher than a lower value ofthe first threshold (this means that the power/charge command is low andwithin the deadband). ‘else’ refers to when the power command ispositive, in which case the system is in discharge mode. if(Pcmd_usr>Pdis_up) checks, when in discharge mode, if thepower/discharge command is greater than an upper value of the of thesecond threshold. elseif (Pcmd_usr<Pdis_lo) checks, when in dischargemode, if the power/discharge command is less than a lower value of thesecond threshold.

In the above-described control logic, the controller compares activeand/or reactive power commands to a threshold. These commands may bereceived by a master controller 400, or autonomously generated by thecontroller 300 itself. The following control logic illustrates anexemplary embodiment in which the active power command is set bycontroller 300 as a function of grid frequency (e.g., using a Hz-Wattfunction). The reactive power command may be set by controller 300 basedon a Volt-Var type function. In the below exemplary control logic, thegrid frequency is compared to a frequency threshold to determine whetherto enter into active mode or active standby mode. The frequencythreshold includes an upper value and a lower value, which form theupper and lower bounds of the deadband.

while(state=runPQ and grid_ok=1)  grid_connect  if (GridFrequency <=minGridF or GridFrequency >=maxGridF)   controlP(FComp(GridFrequency));  active_stdby = OFF;  elseif (GridFrequency > minGridF ANDGridFrequency< maxGridF)   active_stdby = ON;  endif  if (active_stdby =ON)  stop gating;  endif  if(active_stdby = OFF)  start gating;  endifendWhile

For the above control logic, if (GridFrequency<=minGridF orGridFrequency>=maxGridF) refers to the situation where the gridfrequency falls outside of lower and upper values of thethreshold/deadband, in which case active standby is off.controlP(FComp(GridFrequency)) is a control function that sets the powercommand as a function of grid frequency. Fcomp is a function thatreturns a power command based upon grid frequency (e.g., a Hz-Wattfunction). Fcomp can be any known function that returns such a powercommand, and can be a closed loop or open loop function. For example,Fcomp may be a function in which the inverter responds with apredetermined power (e.g., 100% or -100% power) when the grid level isabove or below a certain frequency. Fcomp may be an option that can beenabled by the power system or a user of the power system. For example,the power converter 200 may operate in a normal grid tied mode unlessFcomp is enabled. elseif (GridFrequency>minGridF ANDGridFrequency<maxGridF) refers to the situation where the grid frequencyfalls within the deadband, in which case the inverter is set to output 0kW and active standby is turned on. Example settings for the deadbandrange of FComp could be minGridF=59.7 Hz and maxGridF=60.5 Hz.

In the aforesaid exemplary control logic, the deadband/threshold is afrequency deadband/threshold. In other words, the grid frequency iscompared to upper and lower limits of a deadband/threshold to determinewhether to enter into active standby mode. In another embodiment, thisoperation could be active simultaneously with any of the above controllogic in which the power command is compared to a power deadband. Forexample, the autonomously generated power command set usingcontrolP(FComp(GridFrequency)) could be compared to a powerthreshold/deadband at the same time the grid frequency is compared tothe frequency threshold/deadband.

In the above-described control logic, the controller 300 controls thepower converter 200 to be in active or active-standby mode while thepower converter 200 is synchronized to the grid. In micro-gridapplications, the power system 100 may be connected to the micro-gridand the utility grid at the grid connection 160. The utility grid mayundergo a grid event, such as a power outage, where the power system 100needs to disconnect from the grid and transition to a stand-alone (orislanded) mode during which the power source of the power system 100 isneeded to power the local loads of the micro-grid.

Referring to FIG. 4 the controller may first determine that grid eventoccurs (step 400). The controller may determine that a grid even occursby detecting a grid event using measurements taken by sensors 150. Thegrid event may, for example, be a power outage. The grid event may alsobe based on whether the grid voltage or frequency—which may be measuredby sensors 150—falls outside of predetermined bounds. In an alternativeembodiment, the grid event may be detected by a master controller 400that is coordinating the operations of the micro-grid. The mastercontroller 400 may then send a control signal to controller 300indicating that a grid event has occurred. Upon receipt of the controlsignal, controller 300 determines that a grid event has occurred.

Once controller 300 has determined that a grid event occurs, controller300 sends a control signal to an islanding switch so that the islandingswitch opens and disconnects the power system 100 from the grid (step410). The islanding switch is a separate switch from the grid sideswitch 130. The grid side switch 130 disconnects the power converter 200from the grid connection 160, which includes both the connection to themicro-grid and the utility grid. Differently, the islanding switchdisconnects the power system 100 from the utility grid but not themicro-grid. In an alternative embodiment, master controller 400 may sendthe control signal to the islanding switch rather than controller 300.

Once the power system 100 is disconnected from the utility grid, thepower system 100 is needed to power the local loads of the micro-grid.Thus, if the power system 100 is in the active standby mode, thecontroller 300 controls the power converter to begin gating (step 430)so that power can be supplied to the local loads. Once controller 300determines that the grid is available (step 430), the power system 100can reconnect to the grid (step 440). Once the power converter isreconnected and synchronized to the grid, the controller 300 may againbegin determining whether the power system 100 should be in the activemode or the active-standby mode, by, for example, reverting back to FIG.2B or 3 (step a).

Exemplary control logic for the controller 300 operating the powerconverter 200 in the active and active standby modes in a power system100 capable of operating in an islanding mode includes:

while(state=runPQ and grid_ok=1)  grid_connect  controlP(Pcmd_usr); controlQ(Qcmd_usr);  if (Pcmd_usr >= SupkW or Qcmd_usr >= SupkVAR) active_stdby = OFF;  elseif (Pcmd_usr <= SlokW and Qcmd_usr <= SlokVAR) active_stdby = ON;  endif  if (active_stdby = ON)  stop gating;  endif if(active_stdby = OFF)  start gating;  endif endWhile

The exemplary control logic adds ‘grid_connect’ to the powercontroller's control system. For ‘grid_connect’, the controller 300closes the islanding switch that connects the power system 100 to theutility grid. For disconnecting the power system 100 during a gridevent, the control logic may include:

   if (grid_ok=0 and auto_xfr=1)  state = runUF;  endif endwhilewhile(state=runUF)  grid_disconnect;  start gating;  controlU(Ucmd_usr); controlF(fcmd_usr);  if (grid_ok = 1 and reconnect_time=0  state =runPQ;  endif endwhile

For the above control logic, ‘if (grid_ok=0 and auto_xfr=1)’ is adetermination as to whether there is a grid event (such as an outage)and automatic transfer is turned on (meaning that the system willautomatically transition from grid tied to microgrid mode without userintervention). ‘grid_disconnect’ opens the islanding switch todisconnect the power system 100 from the main utility grid. ‘startgating’ resumes gating if not already on (in other words, if the systemis in active-standby, it exits active-standby and enters active mode).‘controlU(Ucmd_usr)’ is a routine to control power converter outputvoltage to a voltage command. ‘controlF(fcmd_usr)’ is a routine tocontrol output frequency to a frequency command. For ‘if (grid_ok=1 andreconnect_time=0)’, if the grid becomes available and a reconnectcountdown has passed, the power system reverts back to grid-tie mode.

The voltage command and frequency command are commands for the outputvoltage and frequency of the power converter 200. In the above controllogic, these commands are user commands received by controller 300 frommaster controller 400. The voltage command and frequency command mayalso be autonomously generated by the controller 300. The voltagecommand and frequency command are for providing power to the microgrid.The user may wish to modify the output voltage and/or the frequency ofthe power converter 200 during voltage source mode. The user may wish tomake such a change if there is a voltage drop in the local transmissionsuch that the voltage at the load is less than the desired voltage.

The disclosed embodiments provide an power system and method in which anpower converter 200 can be operated in a plurality of modes whensynchronized to a grid. The plurality of modes include an active-standbymode during which the power system's switches 120 and 130 are closed andthe power converter 200 is synchronized to the grid, but thesemiconductor switches of the power converter 200 are not gating. Thepower system's 100 controller 200 controls transition between theactive-standby mode and active mode in an efficient manner by utilizinga deadband/threshold and comparing a power command to thedeadband/threshold. Consistent with the disclosed embodiments of thepresent disclosure, the disclosed power system advantageously has a fastresponse time when transitioning from and idle state to a fully chargingor discharging state. Consistent with the disclosed embodiments of thepresent disclosure, the disclosed power system 100 provides a fastresponse time without incurring the losses typical of having a powerconverter 200 synchronized to the grid while outputting no power. Thedisclosed embodiments provide a power system with a fast response timethat conserves energy.

Although a battery is given as an exemplary power source connected toinput in the aforesaid embodiments discussed in connection with FIGS.2-4 and the aforesaid control logic, it should be understood the presentinvention is not limited to the use of a battery as a power source. Forexample, embodiments of the present invention are suitable for any powersource from which power is not constantly demanded or produced, such asa wind turbine or photovoltaic/solar panels.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed power systemwithout departing from the scope of the disclosure. Other embodiments ofthe present disclosure will be apparent to those skilled in the art fromconsideration of the specification and practice of the presentdisclosure. It is intended that the specification and examples beconsidered as exemplary only, with a true scope of the presentdisclosure being indicated by the following claims and theirequivalents.

1. A power system having a plurality of operating modes including atleast an active mode and an active standby mode, the power systemcomprising: a power converter configured to adapt a power supply to adesired output, the power converter comprising a plurality ofsemiconductor switches, the plurality of semiconductor switchesreceiving a gate signal when the power system is in the active mode suchthat the power converter is in a gating state; a controller forcontrolling the power converter in the active mode and the activestandby mode, the controller being configured to: determine whether thepower system should enter into the active standby mode in which thepower converter is in a non-gating state, when it is determined thepower system should enter into the active standby mode, control thepower converter to be in a non-gating state such that the power systemis in the active standby mode.
 2. The power system of claim 1, whereinthe power converter is coupled between the power source and a powerinverter, and the controller determines whether the power system shouldenter into the active standby mode while the power inverter issynchronized to a grid.
 3. The power system of claim 1, wherein thepower converter is a power inverter coupled between the power source anda grid, and the controller determines whether the power system shouldenter into the active standby mode while the power inverter issynchronized to the grid.
 4. The power system of claim 1, whereinfurther comprising: a power source side switch coupled between the atleast one power source and the power converter and a grid side switchcoupled between the at least one power source and a grid, wherein thepower source side switch and the grid side switch are closed in both theactive mode and the active standby mode.
 5. The power system of claim 4,wherein the power converter is a power inverter coupled between thepower source and the grid, and the controller is further configured toinitialize the power inverter, the controller being configured toinitialize the power converter includes the controller being configuredto: charge a DC bus from the at least one power source; close the powersource side switch; synchronize the power converter to the grid; enterthe power converter into the gating state; close the grid side switchcoupled between the power converter and the grid whereby the powersystem is in a grid-tied mode; and initialize active standby mode tooff.
 6. The power system of claim 1, wherein the at least one powersource includes an energy storage unit, and the power system operates ina discharge state in which the controller controls the power converterto discharge the energy storage unit, a charge state in which thecontroller controls the power converter to charge the energy storageunit, and an idle state, and the controller determines the power systemshould enter into the active standby mode when the power system is in anidle state.
 7. The power system of claim 1, wherein the controller beingconfigured to determine whether the power system should enter into theactive standby mode includes the controller being configured to: comparea power command to a predetermined threshold; determine whether thepower system should enter into the active standby mode according to thecomparison.
 8. The power system of claim 7, wherein the predeterminedthreshold includes an upper threshold value and a lower threshold value,and the controller compares the power command to the lower thresholdvalue when determining whether to enter into active standby mode, andthe power command is compared to the upper threshold value whendetermining whether to enter into active mode.
 9. The power system ofclaim 7, wherein the controller being configured to determine the powersystem should enter into the active standby mode when the power commandis less than a predetermined threshold, and the control system isfurther configured to: determine whether the power system should exitthe active standby mode and enter the active mode by continuing tocompare the power command to the predetermined threshold, and if thepower command exceeds the predetermined threshold, control the powerconverter to be in the gating state.
 10. The power system of claim 1,wherein the controller being configured to determine whether the powersystem should enter into the active standby mode includes the controllerbeing configured to: determine whether the power system is in a chargestate or a discharge state by determining whether a power command ispositive or negative; when it is determined that the power system is inthe charge state, compare the power command to a first predeterminedthreshold, and when it is determined that the power command is higherthan the predetermined threshold, determine that the power system is inan idle state and should enter into the active standby mode; when it isdetermined that the power system is in the discharge state, compare thepower command to a second predetermined threshold, and when it isdetermined that the power command is lower than the second predeterminedthreshold, determine that the power system is in the idle state andshould enter into the active standby mode.
 11. The power system of claim10, wherein the first predetermined threshold includes an upper firstthreshold value and a lower first threshold value, and the secondpredetermined threshold includes an upper second threshold value and alower second threshold value, and when it is determined that the powersystem is in the charge state, the power command is compared to thelower first threshold value to determine whether to enter the activestandby mode, and the power command is compared to the upper firstthreshold value to determine whether to enter into the active mode, andwhen it is determined that the power system is in the discharge state,the power command is compared to the lower second threshold value todetermine whether to enter into the active standby mode, and the powercommand is compared to the upper second threshold value to determinewhether to enter into the active mode.
 12. The power system of claim 1,further comprising: one or more sensors coupled between the powerconverter and the grid to measure real and reactive power; wherein thepower command is determined based on the real and reactive powermeasured by the one or more sensors.
 13. The power system of claim 1,wherein the controller is further configured to receive a user commandfrom a master controller to enter into standby mode, and determine thatthe power system should enter into the active standby mode when the usercommand is received.
 14. The power system of claim 1, wherein thecontroller is configured to perform an AND operation on the gate signaland the result of the determination as to whether the power systemshould enter into the active standby mode.
 15. The power system of claim1, wherein the power converter is coupled between at least one powersource and a utility grid, and the power converter is electricallycoupled to a microgrid having one or more local loads, and thecontroller is further configured to: determine when a grid event occursin the utility grid; open an islanding switch to disconnect the powerconverter from the utility grid when it is determined that the gridevent occurs; and if the power system is in the active standby mode andit is determined that the grid event occurs, enter into the active modesuch that the power converter is gating to supply power to the one ormore local loads.
 16. The power system of claim 1, wherein thecontroller being configured to determine whether the power system shouldenter into the active standby mode includes the controller beingconfigured to: compare a grid frequency to a predetermined threshold;and determine whether the power system should enter into the activestandby mode according to the comparison.
 17. A method for controlling apower system in a plurality of operating modes including at least anactive mode in which a power converter is synchronized to a grid and isin a gating state and an active standby mode in which the power inverteris synchronized to the grid and is not in a gating state, the methodcomprising: comparing a power command to a predetermined threshold anddetermining whether the power system should enter into the activestandby mode based on the comparison; when it is determined that thepower system should enter into the active standby mode, controlling thepower converter to be in a non-gating state.
 18. The method of claim 17,wherein prior to comparing the power command to the predeterminedthreshold, the method further comprises initializing the powerconverter, the initializing comprising: synchronizing the powerconverter to the grid; entering the power converter into the gatingstate; closing a switch coupled between the power converter and the gridsuch that the power system is in a grid-tied mode; and initializingactive standby mode to off.
 19. The method of claim 17, furthercomprising: after determining the power system should enter into theactive standby mode, continuing to compare the power command to thepredetermined threshold to determine whether the power system shouldexit the active standby mode and enter into the active mode.
 20. Themethod of claim 17, wherein comparing a power command to a predeterminedthreshold and determining whether the power system should enter into theactive standby mode based on the comparison comprises: determiningwhether the power system is in a charge state or a discharge state bydetermining whether the power command is positive or negative; when itis determined that the power system is in the charge state, comparingthe power command to a first predetermined threshold, and when it isdetermined that the power command is higher than the predeterminedthreshold, determining that the power system should enter into theactive standby mode; when it is determined that the power system is inthe discharge state, comparing the power command to a secondpredetermined threshold, and when it is determined that the powercommand is lower than the second predetermined threshold, determiningthat the power system should enter into the active standby mode.
 21. Themethod of claim 17, further comprising: receiving the power command froma separate master controller.
 22. The method of claim 17, furthercomprising: determining when a grid event occurs; opening an islandingswitch to disconnect the power inverter from the grid when it isdetermined that a grid event occurs; and if the power system is in theactive standby mode and it is determined that the grid event occurs,entering into the active mode such that the power inverter is gating tosupply power to a local load.
 23. A power inverter system operating in aplurality of modes including at least an active mode and an activestandby mode, the power inverter system comprising: a power inverter forpower conversion between a power source and a grid, the power invertercomprising a plurality of semiconductor switches, the plurality ofsemiconductor switches receiving a gate signal when operating in theactive mode such that the power inverter is in a gating state; acontroller for controlling the power inverter in the active mode and theactive standby mode, the controller being configured to: synchronize thepower inverter to the grid; control the power inverter to be in thegating state in the active mode such that the semiconductor switchesreceive the gate signal; determine whether the power inverter shouldenter into the active standby mode in which the power inverter is in anon-gating state; when in the active standby mode, control the powerinverter to be in a non-gating state.
 24. The power inverter system ofclaim 23, wherein the controller being configured to determine whetherthe power inverter should enter into the active standby mode includesthe controller being configured to: compare a power command to apredetermined threshold; determine whether the power inverter shouldenter into the active standby mode according to the comparison.
 25. Thepower inverter system of claim 24, wherein the controller is furtherconfigured to: while the power inverter is in the active standby mode,compare the power command to the predetermined threshold to determinewhether the power inverter should exit the active standby mode and enterinto the active mode.
 26. The power inverter system of claim 23, whereinthe controller being configured to determine whether the power invertershould enter into the active standby mode includes the controller beingconfigured to: determine whether a power command is positive ornegative; when the power command is negative, compare the power commandto a first predetermined threshold, and when it is determined that thepower command is higher than the predetermined threshold, determine thatthe power inverter should enter into the active standby mode; when thepower command is positive, compare the power command to a secondpredetermined threshold, and when it is determined that the powercommand is lower than the second predetermined threshold, determine thatthe power inverter should enter into the active standby mode.
 27. Thepower inverter system of claim 23, wherein the controller is furtherconfigured to receive a user command from a master controller to enterinto standby mode, and determine that the power inverter should enterinto the active standby mode when the user command is received.
 28. Thepower inverter system of claim 23, wherein the controller is configuredto perform an AND operation on the gate signal and the result of thedetermination as to whether the power inverter should enter into theactive standby mode.
 29. The power inverter system of claim 23, whereinthe controller is further configured to: determine when a grid eventoccurs; and if the power inverter is in the active standby mode and itis determined that the grid event occurs, enter into the active modesuch that the power inverter is gating to supply power to a local load.30. The power inverter system of claim 23, wherein the controller beingconfigured to determine whether the power inverter system should enterinto the active standby mode includes the controller being configuredto: compare a grid frequency to a predetermined threshold; and determinewhether the power inverter system should enter into the active standbymode according to the comparison.